Britain announced in 2014 it had sealed a deal to expand and reinforce its naval presence in Bahrain, allowing it to operate more and bigger ships in the Gulf.

The U.S. Navy’s Fifth Fleet is also based in Bahrain.

The Gulf is a major trade route for oil tankers, its waters shared by Sunni Muslim Arab states and their Shi’ite rival Iran.

Iran and Saudi Arabia support opposite sides in conflicts in Syria, Iraq and Yemen. Bahrain is a close ally of Britain, the United States and Saudi Arabia.

Last year, U.S. Navy commanders accused Iran of jeopardizing international navigation by harassing warships passing through the Strait of Hormuz and said future incidents could result in miscalculation and lead to an armed clash. Iran denied the accusations.